Blasting cap charge



Patented Feb. 25, 1936 PATENT OFFICE- BLASTING CAP CHARGE Charles P. Spaeth, Woodbury, N. J., assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware N Drawing.

7 Claims.

This invention relates to improved compositions for blasting cap charges and more particularly to such compositions having the properties .of high strength and high density desirable in base charges for blasting caps.

Blasting caps, as commonly used in explosive work, may be divided into two general classes,

(l) the so-called ordinary fuse caps, and (2) electric blasting caps. Both types comprise one or more explosive charges contained in a metal shell, the difference being in the method of initiation of the ignition charge. This initiation takes place in the case of fuse caps by means of the fiame resulting from the spit of a fuse, whereas with electric blasting caps it results from the heat developed by the passage of an electric current through a wire of very small diameter.

Blasting caps of all types customarilycontain at least two charges, a secondary or base charge, and a primary charge. The latter may serve as the ignition material or an additional ignition charge may be superimposed on the primary charge. The requirements of the secondary charge of a blasting cap are that it have suflicient detonating ability, and give a sufiiciently high velocity, when detonated, to cause the main explosive charge to function at its maximum elliciency. The primary charge, on the other hand, is necessarily one which picks up rapidly to its maximum velocity in order that a small amount of such charge may be sufficient to detonate properly the base charge, strength being a. secondary consideration. No supplementary ignition charge is required when the primary charge is capable 0. ready and satisfactory ignition by the spit of the fuse or under the influence of a hot electric wire.

The materials used heretofore as base or secondary charges have comprised such explosive trinitrotoluene, pentaerythrite tetranitrate, picric acid, diazodinitrophenol, and the like. The principal primary charges have been mercury fulminate, mixtures of mercury fulm'inate with potassium chlorate, and lead azide. These charges, both primary and secondary, have regularly been employed in compressed form. Additional ignition compositions, loaded above the primary charge, have included lead sulfocyanate mixtures phite compositions, nitrocellulose by itself, and many other compositions, both in compressed and in loose form.

The object of my invention is an improved base 55 charge for blasting caps having highly desirable 'trate, nitrochlorhydrins, and the like.

compounds as tetranitro-methylaniline (tetryl),

with oxidizing agents and fuels, lead hypophos- Application November 8, 1933, Serial No. 697,112 a properties of strength and high density. A further object is such a composition utilizing materials readily available in the explosives-industry and ofknown effectiveness. Additional objects will be disclosed hereinafter. 5

I have found that the foregoing objects are realized by the utilization, assecondary or base charge in blasting caps, of nitrocellulose impregnated" with a liquid nitric ester. Various liquid nitricesters are suitable for the purpose intended,

for example nitroglycerin, ethylene glycol dini- Preferably, however, I employ nitroglycerin as the liquid nitric ester, because of its favorable properties and its availability. Similarly, various kinds of nitrocellulose may be utilized as the material for impregnation. .-I prefer, however, to use nitrocotton, and particularly a. nitrocotton in'the form of smokeless powder in comminuted condition. The material known as Pyro powder, in ground form, has been found to be very satisfactory for use.

The impregnated nitrocellulose material by itself forms an explosive charge that has very desirable properties as a. base charge in-blasting caps. Itposses'ses high potential strength and detonates on explosion with high velocity under the influence of the detonating compounds commonly used as primary charges. It also has a relatively high density, due to the presence of the nitroglycerin as the impregnating material. This high density is of advantage, since it permits the charging of a relatively large amount of the material in a minimum volume, thereby greatly increasing the bulk strength of the charge.

I have found, however, that increased effectiveness is obtained if an inorganic oxidizing salt also is incorporated with the impregnated nitrocellulose. As examples of suitable oxidizing agents for this purpose I may cite sodium nitrate, potassium nitrate, potassium chlorate, potassium perchlorate and thelike. Preferably, however, I use potassium nitratelas such an oxidizing salt.

Various compositions of the ingredients mentioned heretofore may be used. Preferably, how- Smokeless powder 63 Nitroglycerin I 27 Potassium nitrate l 10 Per cent I plosion.

The base charge according to my invention may be used with advantage in both the ordinary 'pregrated with nitroglycerinand potassium ni -trate or other inorganic oxidizing salt, at the base of the shell. A suitable composition for this base charge is 63% smokeless powder, 27%

' nitroglycerin, and 10% potassium nitrate. Above this there will be the primary charge, for 'example lead azide with an ignition charge above the primary charge, this ignition charge being initiated at the time of firing by the passage of the electric current through the wire embedded in the composition. While other amounts of the charge mentioned may "be used, I find it satisfactory to employ-"'5 grains of base charge, 3 grains of primary charge, and 2.5 grains ignition composition.

The base charge, according to invention,-

may be prepared in various ways. I have found an effective method of bringing about the desired results to comprise mixing Pyro powder,

of a suitable screen size, with water in such a manner as to cause it to become thoroughly wet.

Nitroglycerin is then added slowly, while the suspension is agitated for several hours. I find a desirable ratio of the ingredients to be 150 parts by weight of Pyro powder, 675' parts of water, and 66 parts of nitroglycerin. After the agitation of the ingredients in the manner described, the nitrocellulose becomes thoroughly impregnated with the nitroglycerin. The solid material is filtered on a suction filter to a moisture content of around 25%. If desired, the material may be dried and used in this form. Preferably, however, the material is mixed with the inorganic salt, for example potassium nitrate,

a suitable amount of the latter being 24 parts by weight. The water present in the material tends to dissolve the potassium nitrate, bringing about at least a partial impregnation with this salt, as well as with the nitroglycerin. The dried and soreenedmaterial, which is relatively free running and is not at all lumpy in name, is then 0f the nitrocellulose.

nitrocellulose,

- base charge comprises smokeless powder impregin a form suitable for loading into blasting caps.

While I have described my invention in the foregoing in considerable detail, it will be understood that many modifications may be made in the proportion of ingredients used and in the 5 method of treatment, without departing from the scope of the invention. I may also utilize the nitrocellulose impregnated with a liquid nitrate ester as the sole charge, thus serving both as the ignition charge and as the base charge. My invention also contemplates incorporating a stabilizer in the impregnated nitrocellulose composition. I intend therefore to be limited only as indicated in the following patent claims.

I claim: 1

1. A blasting cap composition comprising nitrocellulose impregnated with a liduid explosive nitric ester in an amount less than that of the nitrocellulose.

2. A blasting cap composition consisting solely 2 of nitrocellulose impregnated with a liquid explosive-nitric ester in an amount less than that 3. A blasting cap composition comprising nitrocellulose impregnated with a liquid explosive 2 nitric ester in an amount less than that of the said impregnated nitrocellulose being intimately '-associated with an inorganic oxidizing material. o

4. A blasting cap composition comprising nitrocellulose impregnated with a liquid explosive nitric ester in an amount less than that of the nitrocellulose and with an inorganic oxidizing agent;

5. A blasting cap composition comprising 3 smokeless powder impregnated with nitroglycerin in an amount less than that of the smokeless powder and with an inorganic oxidizing agent. I

6. A blasting cap composition in which the base charge comprises smokeless powder impregnated with nitroclycerin in an amount less than that of the nitrocellulose and potassium nitrate.

7. A blasting cap composition in which the hated with nitroglycerin and potassium nitrate, said impregnated material comprising 40 to smokeless powder, 5 to 35% nitroglycerin, and 2 to 25% potassium nitrate. 4 I

, CHARLES P. SPAETH. 

